Gaps remain in our understanding of the motor system controlling the redirection of the visual axis (gaze) toward novel targets in the periphery. This system must rapidly and accurately move the line of sight by rotating the eyes within the head and the head on the body so that the combined movements place the fovea onto the target. To do so, afferent visual information must be converted into an efferent motor command that is sent to the extraocular and cervical muscles. This project focuses on the role of central Mesencephalic Reticular Formation (cMRF) neurons in the production of such motor signals. While disease of this region is known to cause impairment in the ability to move the eyes and head, little is known about the function and importance of this region in gaze motor control. Initially, the SC encodes target position in terms of distance from the fovea to produce a desired gaze-error signal in a retinal coordinate system. However, this signal cannot be used to drive the disparate eye and head motor plants, and must be first decomposed into separate eye and head signals and converted into appropriate motor coordinates. One possible region involved in these transformations is the cMRF. Single unit recordings from alert monkeys free to move their eyes and head will be made during gaze shifts to visually presented targets. In order to characterize cMRF neurons, several behavioral paradigms and analytical techniques will be used. Gaze shifts will be performed from different initial head and eye positions in order to assess the role of cMRF neurons in head and eye motor control. Movements from various eye-in-head and head- on-body positions will be used to distinguish the possible coordinate systems encoded by these neurons. Finally, simultaneously recorded cervical EMG activity will be correlated with neuronal discharge. Cells will be analyzed in terms of eye and head movement dynamics (position, velocity, acceleration) to determine what information is encoded in the temporal characteristics of the spike train. Characterization of this region will allow better understanding of the motor deficits observed in clinical disease.